The invention relates to a hermetic reciprocating piston compressor, and in particular to a compressor having shock and vibration absorbing mounts that vertically suspend the compressor unit within its housing.
In most hermetic compressors, the motor compressor assembly is vertically supported within the housing by means of helical springs such that vibrations from the torque reaction caused by starting and stopping the compressor are absorbed by lateral deflection of the springs. Each of these springs is sufficiently stiff to withstand the lateral forces of the torque reaction while still being soft enough to provide vibration isolation. The springs deflect in a vertical direction to reduce vibrations transmitted to the compressor housing. The spring constant of each spring determines the amount of force transferred to the external connections of the compressor which is related to the sound transmitted out of the system.
Because of the necessity of controlling both vertical and horizontal motion, prior helical springs have been constructed with higher spring constants than would have been necessary if the helical springs were designed to only damp vertical vibrations. If the helical spring only had to damp vertical motion it could be made softer (i.e. with a lower spring constant) and therefore reduce sound transmission to the housing.
The problem with prior art spring mounting systems, such as that shown in U.S. Pat. No. 3,531,069 is that they do not adequately control the oscillations and sound transmittance of the motor compressor unit during starting and stopping, especially in large compressors. Sound transmittance is normally greater the larger the compressor. Horizontal oscillations about the shaft of the springs may result in over stressing and failure of the springs and other compressor components. The aforementioned prior art patent utilizes two helical springs to attempt to solve the sound transmittance problem and control horizontal displacement. An inner spring is used for controlling vertical movement while an outside larger, helical spring is used to control lateral displacement. A particular problem of this combination is of impact of the outside spring against the inner spring or mounting bracket during torsional movement accompanying the starting or stopping of the compressor. These impacts increase the noise transmitted through the compressor housing.
Also there is a certain horizontal displacement of the compressor where there is no damping of horizontal vibrations. The outside spring initially is not in contact with either the inner spring or mounting bracket therefore no damping takes place at compressor startup or shutdown.
Another prior art shock mount is disclosed in U.S. Pat. No. 1,988,295 which describes a yieldable supporting structure for use in eliminating vibratory motions of shock mount springs. This patent utilizes a helical spring to support a machine element with an overlying clip to reduce and dampen vibratory motions of the spring. The clip is attached to one of the machine members and biasedly contacts and overlies the helical spring. In this way, the force of the clip is used to reduce vibratory motions of the helical spring. A problem with this design is that by reducing the vibrations of the spring in this matter, the spring system may have a larger resultant spring constant, which would thereby transmit more energy to the compressor housing and correspondingly increase sound transmittance.
Another problem with the design of U.S. Pat. No. 1,988,295 is that lateral deflection of the shock mount is not as small as which could be achieved. The clip is in contact with the helical spring up until a point before where the spring meets the opposing support. Because the clip rides on the helical spring, there is a flexible object on which the clip may contact and which will not counteract the lateral deflection of the shock mount. Particularly, during lateral deflection of the shock mount, the shock mount will bend more at the location of the helical spring just beyond the end of the legs of the clip causing premature failure.
What is needed is a spring mounting system which dampens excessive horizontal oscillations and eliminates impact noise during starting and stopping. The spring mounting system must not utilize thicker springs, thereby not increasing transmission or there exists a need for a shock mount to withstand the higher horizontal vibrational forces encountered in larger compressors.
The present invention is directed to overcoming the aforementioned problems associated with prior shock mounts for use in larger compressors, wherein it is desired to utilize a helical spring for reduction of vertical vibrations and a formed flat spring for control of horizontal vibrations.